Feldspathic Wacke Research Articles

Provenance and tectonic setting of greywacke and siltstone of the Nampala gold deposit, Southern Mali

The petrographical and geochemical analyses of greywacke and siltstone samples from the Nampala gold deposit of the Paleoproterozoic Birimian supergroup, Southern Mali, have been carried out to make inferences on the provenance, tectonic settings, and weathering history of the sediments. Petrographical investigations revealed that greywackes can be classified as feldspathic wackes, with immature to moderately mature sediments, with the siltstones being immature. Geochemically, greywackes show features that resemble typical wacke sedimentary rocks, whereas the siltstones are arkose to litharenite. Overall, Nampala sedimentary rocks experienced low intensity of paleoweathering with <70 CIA and <90 CIW values and have not undergone significant sediment recycling having >1 CIV values. Their quartz and feldspar contents, together with the ratio of Al2O3/TiO2 and La/Sc, suggest the derivation of sediments from felsic igneous rocks, with a possible minor contribution from mafic proto-source rock. The petrographic and geochemical features of the greywackes and siltstones are consistent with siliciclastic rocks formed in an active continental margin, similar to other sedimentary rocks of the Paleoproterozoic Birimian terrane. These findings put positive constraints on the subduction-accretion geodynamic model proposed for the evolution of the Birimian terrane of the West African Craton.

Mineralogical Characteristics of Greywackes at Lake Bosomtwe Area in the Ashanti Region of Ghana

The mineralogical content and texture of greywackes in the Lake Bosomtwe area of Ghana’s Ashanti Region are examined in this petrographic study. The Graywackes are fine- to medium-grained, poorly sorted, firmly indurated sedimentary rocks. Quartz is the dominant framework component of the studied specimens, and it is both monocrystalline and polycrystalline. The average mineral compositions of the samples are quartz (53%), feldspar (16%), biotite (4%), opaque minerals (2%), and lithic fragments (1%) and classified as feldspathic wacke. The other predominant minerals include orthoclase and plagioclase feldspars. Other constituents include biotite, opaque minerals, and iron oxides. The characteristics of an advanced sedimentary environment with moderate mobility are evident in the rocks. The discoveries broaden our understanding of the Ashanti Region’s geology and have ramifications for resource development, environmental management, and geological study.

Integrated geophysical, petrophysical and petrographical characterization of the carbonate and clastic reservoirs of the Waihapa Field, Taranaki Basin, New Zealand

Despite the economic importance of the Waihapa Field in Taranaki Basin in New Zealand, the structural setting, petrographic and petrophysical properties of its Cenozoic reservoirs are still poorly understood. This research integrates a 3D seismic survey with core and well logs data, as well as petrographic description in order to discuss the structural setting and the reservoir characterization of the Cenozoic reservoirs along the Waihapa Field, Taranaki Basin, New Zealand. A major thrust fault was interpreted dissecting both the Kapuni (Paleocene- Eocene) and Ngatoro (Oligocene- Early Miocene) groups and another opposite thrust fault affecting the Ngatoro Group and the Waihapa anticline. These compressional structures were resulted from the regional compression which affected the Taranaki Basin during the Miocene. Wai-iti Group (Miocene) is dissected by a set of NE-SW normal faults. These normal faults remark the end of the compressional phase and the beginning of a new extensional phase along the Taranaki Basin.The petrographic data of the studied reservoirs indicate that the Late Miocene Mount Messenger Formation is composed of feldspathic wacke, micaceous feldspathic quartz arenite and mudstone microfacies, whereas the Oligocene Tikorangi Formation is composed of five microfacies (bioclastic grainstone, bioclastic packstone, sandy wackestone, highly fractured silty mudstone and sandy glauconitic packstone microfacies). Downward, the Upper Eocene Mangahewa Formation is composed of ferruginated quartz arenite, micaceous quartz arenite, and ferruginated calcareous quartz arenite microfacies. Cementation and compaction are mostly affected the Mangahewa Formation while fracturing and dissolution are primarily affected the Tikorangi and the Mount Messenger formations respectively. The studied core data was discriminated into four petrophysical static rock types (PSRTs). The PSRT1, representing the Mount Messenger reservoir, has the best reservoir quality (av. porosity = 23.3%, av. permeability = 45.0 md, and meso pores, 2.60 μm) while the PSRT4 of Tikorangi Formation has the lowest reservoir quality (av. porosity = 5.5%, av. permeability = 0.01 md, and nano pores, 0.07 μm). The PSRT2 (av. porosity = 4.17%, av. permeability = 0.26 md, and micro pores, 0.59 μm) and PSRT3 (av. porosity = 5.93%, av. permeability = 0.08 md, and micro pores, 0.22 μm) are petrophysically considered transitional rock types between the PSRT1 and the PSRT4.However, Tikorangi reservoir is already producing oil from the borehole scale fractures. This work represents the workflow applied during integrating seismic, petrographical and petrophysical data in order to characterize carbonate and clastic reservoirs for any further hydrocarbon development plans along the field.

Sedimentology, petrography, hydraulic flow units, and reservoir quality of the bayhead delta reservoirs: Late Messinian Qawasim formation, Nile Delta, Egypt

Bayhead sandstone reservoirs are challenging due to their complexities and limited examples. This paper focused on the characteristics of the bayhead sandstone reservoirs and their heterogeneities based on an integrated sedimentological, petrographical, and petrophysical aspects that controls the exploration and development for these reservoirs. This study uses an example from Manzala Gas Field (Eastern Nile Delta). In this study, the sedimentological and petrographical analyses are employed to understand the internal textures and architecture as well as meso- and microscopic heterogeneities of the bayhead delta reservoirs. This is integrated with the petrophysical characteristics and neural network techniques to characterize hydraulic flow units of bayhead delta reservoir using core, borehole image, and log data. The bayhead delta (bay fill) reservoir consists of five main sedimentary sub-environments include main distributary channel, proximal and distal crevasse splays, and crevasse channels, as well as bayhead delta lobes. The distributary channel represents the highest reservoir quality (units 3 and 4), followed by crevasse channel (unit 3 and 2); bayhead delta front lobes (units 2 and 1), and the lowest quality crevasse splays (unit 1). On microscale, the bayhead delta reservoir is characterized by wide spectrum of lithofacies from quartz arenite to feldspathic wacke. The depositional setting is important controlling factor on the reservoir quality that altered by the diagenetic processes. They include the anhydrite, quartz, carbonate, and chlorite, and kaolinite cements as well as dissolution of quartz, feldspar, bioclast, and carbonate grains. This study enhances the understanding of the of the bayhead distributive system heterogeneities and prediction of bay fill facies reservoirs to improve the exploration and development of that targets.

Petrography, geochemistry, and Nd isotope systematics of metaconglomerates and matrix-rich metasedimentary rocks: implications for the provenance and tectonic setting of the Labrador Trough, Canada

The New Quebec Orogen consists of a supracrustal belt that was reworked when the Superior Craton collided with the Core Zone terrane during the Paleoproterozoic Trans-Hudson Orogeny. Within the New Quebec Orogen, the Kaniapiskau Supergroup can be divided into four terrigenous lithotypes metamorphosed at low-grade: one set with greater compositional and textural sedimentary maturity classified as quartz arenites and subarkoses, and another set with lower textural maturity classified as feldspathic wackes and mudrocks. In contrast, the Laporte Group includes homogeneous lithotypes represented by feldspathic and lithic wackes with a range of matrix contents metamorphosed at low to medium grade. The Kaniapiskau Supergroup rocks have a wide range of SiO2 and Al2O3 contents (SiO2/Al2O3 = 3.7–51) compared to the restricted compositional range of the Laporte Group rocks (SiO2/Al2O3 = 4.4–6.8). In general, the geochemical variations in both formations of the Laporte Group are within the range of the main clast varieties from basal metaconglomerates, although the Deborah Formation (top unit) records higher TiO2, P2O5, MgO, and Ni contents and high Cr/Th, Co/Ba, Th/U, and Rb/Sr ratios indicating additional mafic sources. Our results support the hypothesis that the Kaniapiskau Supergroup was deposited along an intraplate continental margin with predominantly recycled (εNd(1.87Ga) –12) Paleoarchean sources (TDM 3.2 Ga). In contrast, the Laporte Group marks the transition from a continental forearc (Grand Rosoy Fm.) with a typical juvenile source, including granitic clasts (εNd(1.83Ga) –0.1 to +3.1), to a wedge-top depozone (Deborah Fm.) in the context of a collisional proforeland basin. This syncollisional sedimentary environment is characterized by the presence of old crustal components (εNd(1.83Ga) –4.4 to –9.1).

Depositional sub-environment of Gombe Sandstone in Kumo and its environs, part of Gongola Basin, Northern Benue Trough, Northeastern Nigeria

Evaluation of Gombe Formation in the area around Kumo part of Gongola arm was carried out with a view to determine its depositional sub environment in the area through detailed geologic mapping, litholog construction and petrographic as well as sieve analyses of the sandstone samples. Detailed geologic mapping in the study was carried out hence the production of the geologic map of the area. Other pertinent geologic information such as color, texture, sedimentary structures, thicknesses of different beds and their vertical and lateral changes were determined. Four samples each were collected and subjected to laboratory analyses (i.e sieve analysis and petrography). Three stream sections were identified and logged in the field and plotted using sed log computer program. The sections include Kandahar stream section where a sequence of sandstones, mudstone and ironstone of Gombe Formation along a stream channel with a total thickness of 5.2 m is recognized; the GRA stream section where strata of Gombe Formation with a thickness of 2.06 m comprising sandstone, mudstone and ferriginized sandstone caping were logged and the Jauro Bose stream section where strata with a total thickness of 2.0 m comprising of sandstones and ferriginized reddish brown sandstone and mudstone with ferriginized sandstone interbeds. The Gombe Formation in the study area is characterized by yellow to brown sandstones with interbedded mudstones, ferriginized sandstones and ironstones. Grain size analysis indicate that the sandstones of Gombe Formation in the study area is fine to very fine grained, moderately well sorted, strongly coarse skewed and leptokurtic to very leptokurtic. Petrographic results indicate that all the analyzed samples contain large percentages of quartz in excess of 65 – 71 % with greater than 10% matrix and are characterized by angular to subrounded grains of quartz, feldspar and rock fragment and fall within the domain of feldspathic wacke and lithic wacke in the QFL diagram for sandstone classification scheme. Field evidences like interbeds of mudstones within the sandstone beds, flaser beddings, parallel laminations and bioturbations suggest that the sandstones were deposited in a transitional environment influenced by tides. Additional evidence is observed from laboratory analyses results especially sieve analysis that indicate fine to very fine grained sands and moderately well sorting, coupled with the characteristic shapes and the level of maturity obtained from the petrographic results like the large percentage of quartz and the subangular to subrounded grains. Integrating the field evidences and the laboratory results, the depositional sub environment for the Gombe Formation in the study area is interpreted to be intertidal environment of tidal flat of an estuary.

Modal composition and tectonic provenance of the sandstones of Ecca Group, Karoo Supergroup in the Eastern Cape Province, South Africa

AbstractPetrography of the sandstones of Ecca Group, Karoo Supergroup in the Eastern Cape Province of South Africa have been investigated on composition, provenance and influence of weathering conditions. Petrographic studies based on quantitative analysis of the detrital minerals revealed that the sandstones are composed mostly of quartz, feldspar and lithic fragments of metamorphic and sedimentary rocks. The sandstones have an average framework composition of 24.3% quartz, 19.3% feldspar, 26.1% rock fragments, and 81.33% of the quartz grains are monocrystalline. These sandstones are generally very fine to fine grained, moderate to well sorted, and subangular to subrounded in shape. In addition, they are compositionally immature and can be classified as feldspathic wacke and lithic wacke. The provenance characteristics suggest the influence of plutonic and metamorphic terrains (meta-magmatic arc) as the main source rock with minor debris derived from recycled sedimentary rocks. The latter revealed that the compositional immaturity of the sandstones is a result of weathering or recycling and short transport distance. The weathering diagrams and semi-quantitative weathering index indicate that the Ecca sandstones are mostly from a plutonic source area, with climatic conditions ranging from arid to humid. The detrital modal compositions of these sandstones are related to back arc to island and continental margin arc. These results, therefore, support previous studies that infer foreland basin setting for the Karoo Basin.

Siltstones Across the Daptocephalus ( Dicynodon ) and Lystrosaurus Assemblage Zones, Karoo Basin, South Africa, Show No Evidence For Aridification

Abstract: Changes in the record of vertebrate-assemblage zones in the Karoo Basin, South Africa, serve as a model for the response of terrestrial ecosystems to the end-Permian biotic crisis. Vertebrate turnover from the Daptocephalus to Lystrosaurus Assemblage Zone is believed to have begun with the appearance of subtle siltstone-color variance and is coeval with a unique, laminated lithofacies, both of which are interpreted by other workers to represent evidence for an aridification trend. The laminated facies consists of interbedded greenish-gray and dark reddish-gray siltstone, with coloration of the latter reported as a function of an increasing eolian component. The current study combines stratigraphy, petrography, geochemistry, and rock magnetic properties of an interlaminated succession and lateral equivalents at Old Lootsberg Pass in the Eastern Cape Province to determine whether such subtle color variance is a function of aridification and, hence, climate change. Siltstones were evaluated from intervals both below and above a pedogenic nodule-bearing feldspathic wacke that is physically correlated over a > 0.5 km distance. The lower succession consists of interbedded greenish-gray ( sensu latu ) and reddish-gray ( sensu latu ) siltstone in which undisturbed and minimally disturbed primary sedimentary, along with few secondary biogenic structures, are interpreted to represent deposition in an abandoned channel-fill complex. Massive greenish-gray and dark reddish-gray siltstone above the channel complex demonstrate that coloration is variable across laterally equivalent strata. Both lithologies were assessed using X-ray fluorescence, X-ray diffraction, Mossbauer spectroscopy, scanning electron microscopy with EDS, and bulk magnetic susceptibility, stepwise acquisition of an isothermal remanent magnetization (IRM), and backfield direct field demagnetization. Our data indicate that there is no statistically significant difference in major-element concentrations between lithologies and that subtle color difference is a function of the presence of fine ( Lystrosaurus Assemblage Zone was not arid. In contrast, the landscape was wet, that allowed for the continued growth of a Permian-age flora under conditions of high water table that experienced temporal fluxes in the hydrological regime promoting spatial color modification of sediment.

Two flysch belts having distinctly different provenance suggest no stratigraphic link between the Wrangellia composite terrane and the paleo-Alaskan margin

The provenance of Jurassic to Cretaceous flysch along the northern boundary of the allochthonous Wrangellia composite terrane, exposed from the Lake Clark region of southwest Alaska to the Nutzotin Mountains in eastern Alaska, suggests that the flysch can be divided into two belts having different sources. On the north, the Kahiltna flysch and Kuskokwim Group overlie and were derived from the Farwell and Yukon-Tanana terranes, as well as smaller related terranes that were part of the paleo-Alaskan margin. Paleocurrent indicators for these two units suggest that they derived sediment from the north and west. Sandstones are predominantly lithic wacke that contain abundant quartz grains, lithic rock fragments, and detrital mica, which suggest that these rocks were derived from recycled orogen and arc sources. Conglomerates contain limestone clasts that have fossils matching terranes that made up the paleo-Alaskan margin. In contrast, flysch units on the south overlie and were derived from the Wrangellia composite terrane. Paleocurrent indicators for these units suggest that they derived sediment from the south. Sandstones are predominantly feldspathic wackes that contain abundant plagioclase grains and volcanic rock fragments, which suggest these rocks were derived from an arc. Clast compositions in conglomerate south of the boundary match rock types of the Wrangellia composite terrane.

Diagenesis and Provenance of Lati Sandstones in the Berau Area, East Kalimantan Province, based on Petrography Data

DOI: 10.17014/ijog.v7i3.143This study is focused on the provenance and diagenetic processes affecting the sandstones of Lati Formation cropping out at Berau Area, East Kalimantan Province. Petrographic analysis of twenty-two samples from this formation shows that these sandstones are classified as litharenite, feldspathic litharenite, sublitharenite, feldspathic wacke, and lithic wacke, which are partially calcareous. Preserved diagenetic processes were visible on the petrographic analysis including cementation, replacement, dolomitization, compaction, and dissolution. The provenance of these sandstones is dominated by granitic rocks initiated from tectonic setting of rifted continental margin, transported toward southeast.

Diagenesis and Provenance of Lati Sandstones in the Berau Area, East Kalimantan Province, based on Petrography Data

DOI: 10.17014/ijog.v7i3.143 This study is focused on the provenance and diagenetic processes affecting the sandstones of Lati Formation cropping out at Berau Area, East Kalimantan Province. Petrographic analysis of twenty-two samples from this formation shows that these sandstones are classified as litharenite, feldspathic litharenite, sublitharenite, feldspathic wacke, and lithic wacke, which are partially calcareous. Preserved diagenetic processes were visible on the petrographic analysis including cementation, replacement, dolomitization, compaction, and dissolution. The provenance of these sandstones is dominated by granitic rocks initiated from tectonic setting of rifted continental margin, transported toward southeast.

Diagenesis of Cotton Valley Sandstones, Catahoula Creek Field, Southern Mississippi: ABSTRACT

Three conventional cores from the deep Cotton Valley clastics in south Mississippi were analyzed by thin-section petrography, scanning electron microscopy, x-ray diffraction, and cathodoluminescence. The ^dgr13C and ^dgr18O values were determined on carbonate cements in sandstones. The sandstones are predominantly subarkose, arkose, and quartzarenites, with minor amounts of quartz and feldspathic wackes. K-feldspar, muscovite, and plagioclase are relatively fresh. Authigenic clay in sandstones is almost exclusively chlorite that occurs as a pore-lining and pore-filling phase, most commonly associated with porous zones. Feldspar diagenesis includes overgrowths of both potassic feldspar and albite. Typically, fresh detrital K-feldspar grains have overg owths of K-feldspar that are partly dissolved, whereas plagioclase grains (with partly dissolved interiors) have unaltered albite overgrowths. Quartz overgrowth development is pervasive where not hindered by chlorite. Carbonates include intergranular calcite, dolomite, and iron-rich dolomite. The earliest phase is a pore-lining dolomite cement, followed by a later ferroan calcite. Ferroan dolomite (or ankerite) is associated with chlorite in relatively porous intervals. The ^dgr13C values of mixed carbonates in sandstones range from -0.8 to -4.4^pmil (PDB), which is typical of normal marine carbonates. The ^dgr18O values range from -5.0 to -12.3^pmil (PDB). Formation temperatures of approximately 115° -160°C are suggested by the oxygen isotope data from al ost pure late-stage ferroan dolomite. Petrographic evidence suggests that coarser grained sands were cemented early in the burial history by dolomite and calcite. These cements were later leached by formation waters, possibly related to the generation of organic acids and/or carbon dioxide released during kerogen maturation. Resultant secondary porosity was preserved by formation of bladed chlorite. The source of the iron, manganese, and magnesium necessary for chlorite formation was presumably the release of ions from smectite to illite conversion in shales, because ferromagnesian rock fragments in the sandstones are rare. The feldspar volume and stability and the ^dgr13C values of carbonate cements suggest the pore water was probably initially seawater and later brine that migrated upward from the Louann Salt Present brines contain 7,300 ppm of potassium and 51,113 ppm of sodium. Meteoric diagenesis of these rocks was likely minimal. These data suggest that original depositional porosities and permeabilities and carbonate cementation are significant controls in secondary porosity formation in the Cotton Valley sandstones. End_of_Article - Last_Page 1424------------

Biotite Variation as a Guide to Petrogenesis of Granitic Rocks in the Pre-Cambrian of Northeastern Alberta

Information about internal variation in a band of foliated granitic rocks in the Pre-Cambrian of northeastern Alberta has been obtained by mapping variation in biotite refractive index on the basis of 430 determinations distributed throughout the northern portion of the band. In many parts of the area isopleths of the biotite refractive index parallel the regional foliation, whereas refractive index does not vary in other portions of the area. A correlation coefficient of 0·804 between refractive index and Fe:Mg ratio in seven analysed biotites supports the contention that refractive index can be used as a measure of relative Fe:Mg ratio in this suite of related biotites. Of the factors that control the Fe:Mg ratio in biotites, variation in oxygen partial pressure is the most important in this particular geological situation. As a result, the pattern of refractive index variation reflects the pattern of variation in oxygen partial pressure at the time of formation of the biotite. In the light of this relationship, the isopleths that parallel the foliation in many areas are interpreted as relics of an original system consisting of individual layers that were closed systems with respect to oxygen partial pressure. The areas of uniform refractive index have been subject to a continuous vapor phase which equalized oxygen partial pressures throughout the area. This vapor phase could be of magmatic origin or could arise during progressive metamorphism. Field relations and chemical and mineralogical variation within and around this group of rocks are consistent with this interpretation and further suggest that the granitic rocks were derived from a mixed suite of intermediate to basic volcanic rocks, tuffaceous metasediments, and feldspathic wackes by metamorphic recrystallization and accompanying homogenization of these materials.